[SOLVED] Strange Problem in Keil?

[dariush_abbasi]

Hi dear friends.
I have a strange problem :
when i use this code :

int Whole = 0;
int On = 0;
int Percent = 0;
int Temp ;

   On = 42;
   Whole = 100;
   Percent   = (On*100) / Whole;
   Temp = Percent;

The LCD shows 42 which is normal.
but using this code:

int Whole = 0;
int On = 0;
int Percent = 0;
int Temp ;

   On = 42;
   Whole = 100;
   Percent   = (On / Whole)*100;
   Temp = Percent;

The LCD shows 00 which i can't figure out why!

 

[alexxx]

The LCD shows 00 which i can't figure out why!

case 1:
(On*100)/Whole = (42*100)/100 = 4200/100 = 42

case 2:
(On/Whole)*100 = (42/100)*100 = 0*100 = 0

You are not using float variables and the intigers are not capable of holding floating point values. No approximation takes place. All the floating points are going bye bye. Even if the result was 0.999999, you would get 0 as well. This is how C works.


Hope that helped,
Alexandros

 

[ace1903]

Percent = (On / Whole)*100;
First (On/Whole) is evaluated. Since all elements and result are integer, result of division is rounded 42/100=>0 and 0*100=0
In firs case On*100=42*100=4200 and 4200/100 =42

 

[p.luc]

I believe it's evaluating from left-to-right and may have something to do with Operator associativity (Operator associativity - Wikipedia, the free encyclopedia).

(on / whole) * 100 = (42 / 100) * 100 = 0 * 100 = 0

 

[bigdogguru]

I have a strange problem :
when i use this code :

int Whole = 0;
int On = 0;
int Percent = 0;
int Temp ;

   On = 42;
   Whole = 100;
   Percent   = (On / Whole)*100;
   Temp = Percent;

The LCD shows 00 which i can't figure out why!

The result displayed, 00, is the expected result.

The issue is the following line:

Percent   = (On / Whole)*100;

If you evaluate it in order of precedence:

On / Whole = 42 / 100 = 0

0 * 100 = 0

Therefore Temp = Percent = 0, such is the case with integer math. Of course if either the variable "On" or "Whole" were floating point, then the result would be:

Temp = Percent = 42

BigDog

 

[dariush_abbasi]

Thanks a lot.